Exhaust treatment system

ABSTRACT

An exhaust gas treatment system of an internal combustion engine includes a selective catalytic reduction catalyst fluidly connected to the internal combustion engine, an oxidation catalyst fluidly connected upstream of the selective catalytic reduction catalyst, and a particulate filter fluidly connected upstream of the selective catalytic reduction catalyst. The exhaust gas treatment system further includes a recirculation line configured to direct a portion of an exhaust flow of the internal combustion engine toward an inlet of the engine.

TECHNICAL FIELD

The present disclosure relates generally to an exhaust treatment systemand, more particularly, to an exhaust treatment system having aselective catalytic reduction (“SCR”) catalyst.

BACKGROUND

Internal combustion engines, including diesel engines, gasoline engines,natural gas engines, and other engines known in the art, may emit anexhaust flow containing a complex mixture of solid, liquid, and gaseouscomponents. For example, the gaseous components of the exhaust flow mayinclude compounds such as nitrous oxides (“NOx”) and CO, and the solidand/or liquid components of the flow may include soluble organicfraction, soot, and/or unburned hydrocarbons. Together, the solubleorganic fraction, soot, and unburned hydrocarbons emitted by internalcombustion engines is generally referred to as particulate matter.

The Environmental Protection Agency regulates the emissions releasedinto the atmosphere from such engines based on the type, size, and/orclass of engine. These exhaust emission standards continue to becomemore stringent, and engine manufacturers have begun to use catalyticexhaust treatment systems to comply with these regulations. In suchsystems, a reductant, such as urea or ammonia, may be injected into theexhaust gas upstream of an SCR catalyst, and the catalyst materialswithin the SCR catalyst may reduce NOx carried by the exhaust gas in thepresence of the reductant. In addition, a particulate filter may capturea portion of the particulate matter carried by the exhaust.

The effectiveness of an SCR catalyst is based on its ability to convertNOx carried in the exhaust gas to N₂ and other gaseous species such asO₂ and H₂O. Maintaining the SCR catalyst within a desired temperaturerange and providing it with a flow of exhaust gas having approximately aone-to-one ratio of NO to NO₂ are both factors that assist in maximizingthe NOx conversion rate of the SCR catalyst. The exhaust gas leaving theengine, however, typically contains a much higher percentage of NO thanNO₂. Thus, exhaust treatment systems often include an oxidation catalystdisposed upstream of the SCR catalyst to assist in oxidizing the NOpresent in the exhaust gas. Oxidizing the NO may increase the amount ofNO₂ present in the exhaust gas entering the SCR catalyst and mayfacilitate achieving a one-to-one ratio of NO to NO₂.

An exhaust treatment system for controlling the NOx and particulatematter emissions of an internal combustion engine is illustrated in U.S.Pat. No. 6,928,806 (“the '806 patent”). Specifically, the '806 patentdiscloses an oxidation catalyst, an SCR catalyst coupled downstream ofthe oxidation catalyst, and a particulate filter coupled downstream ofthe SCR catalyst.

Although the system disclosed in the '806 patent may assist in removingparticulate matter and reducing the NOx content of the exhaust gas, theSCR catalyst of the '806 patent is disposed upstream of the particulatefilter and is, therefore, particularly susceptible to fouling from, forexample, particulate matter carried in the exhaust flow.

In addition, the system of the '806 patent fails to take advantage ofthe benefits associated with the use of exhaust gas recirculation(“EGR”) to direct at least a portion of the exhaust gas into the intakeair supply of the engine. The use of EGR may assist in reducing theconcentration of oxygen within the cylinder and increasing the specificheat of the air/fuel mixture, thereby reducing the amount of NOxproduced by the engine. The use of EGR in combination with SCR catalysttechnology may also assist in improving the fuel economy of the enginesystem and may increase the amount of NO₂ produced by the enginerelative to NO. The system of the '806 patent is not configured todirect any portion of the exhaust gas back to the intake of the engineto reduce NOx formation, improve fuel economy, or increase the quantityof NO₂ produced by the engine.

The disclosed exhaust treatment system is directed to overcoming one ormore of the problems set forth above.

SUMMARY OF THE INVENTION

In one embodiment of the present disclosure, an exhaust gas treatmentsystem of an internal combustion engine includes an SCR catalyst fluidlyconnected to the internal combustion engine, an oxidation catalystfluidly connected upstream of the SCR catalyst, and a particulate filterfluidly connected upstream of the SCR catalyst. The exhaust gastreatment system further includes a recirculation line configured todirect a portion of an exhaust flow of the internal combustion enginetoward an inlet of the engine.

In another embodiment of the present disclosure, an exhaust gastreatment system of an internal combustion engine includes an SCRcatalyst fluidly connected to the internal combustion engine, anoxidation catalyst fluidly connected upstream of the SCR catalyst, and aparticulate filter fluidly connected upstream of the SCR catalyst. Thesystem further includes a low pressure exhaust gas recirculation loop.

In yet another embodiment of the present disclosure, a method of anexhaust flow of an internal combustion engine includes filtering theexhaust flow with a particulate filter, oxidizing the exhaust flow withan oxidation catalyst, catalytically reducing NOx contained in thefiltered oxidized flow with an SCR catalyst, and directing a portion ofthe exhaust flow to an inlet of the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of an engine having an exhausttreatment system according to an exemplary embodiment of the presentdisclosure.

FIG. 2 is a diagrammatic illustration of an engine having an exhausttreatment system according to another exemplary embodiment of thepresent disclosure.

FIG. 3 is a diagrammatic illustration of an engine having an exhausttreatment system according to still another exemplary embodiment of thepresent disclosure.

FIG. 4 is a diagrammatic illustration of an engine having an exhausttreatment system according to yet another exemplary embodiment of thepresent disclosure.

DETAILED DESCRIPTION

FIG. 1 illustrates a power source 12 having an exemplary exhausttreatment system 10. The power source 12 may include an engine, such as,for example, a diesel engine, a gasoline engine, a natural gas engine,or any other engine apparent to one skilled in the art. The power source12 may alternatively include another source of power, such as a furnaceor any other source of power known in the art.

The exhaust treatment system 10 may be configured to direct exhaustgases out of the power source 12, treat the gases, and introduce aportion of the treated gases into an inlet 21 of the power source 12.The exhaust treatment system 10 may include, for example, an NOx trap35, an energy extraction assembly 22, a regeneration device 20, anoxidation catalyst 18, a filter 16, an SCR catalyst 19, and/or aclean-up catalyst 33. The exhaust treatment system 10 may furtherinclude a recirculation line 24 fluidly connected between the filter 16and the SCR catalyst 19. Alternatively, the recirculation line 24 may befluidly connected between the oxidation catalyst 18 and the filter 16,between the SCR catalyst 19 and the clean-up catalyst 33, or downstreamof the clean-up catalyst 33. The exhaust treatment system 10 may stillfurther include a flow cooler 26, a flow sensor 28, a mixing valve 30, acompression assembly 32, and an aftercooler 34.

A flow of exhaust produced by the power source 12 may be directed fromthe power source 12 to components of the exhaust treatment system 10 byflow lines 15. It is understood that the power source 12 may include oneor more combustion chambers (not shown) fluidly connected to an exhaustmanifold. In such an exemplary embodiment, the flow lines 15 may beconfigured to transmit a flow of exhaust from the combustion chambers tothe components of the exhaust treatment system 10 via the exhaustmanifold. The flow lines 15 may include pipes, tubing, and/or otherexhaust flow carrying means known in the art. The flow lines 15 may bemade of alloys of steel, aluminum, and/or other materials known in theart. The flow lines 15 may be rigid or flexible, and may be capable ofsafely carrying high temperature exhaust flows, such as flows havingtemperatures in excess of 700 degrees Celsius (approximately 1,292degrees Fahrenheit).

The NOx trap 35 may be any type of NOx adsorber or absorber known in theart, such as, for example, a lean NOx trap, and may contain catalystmaterials capable of absorbing, adsorbing, and/or otherwise storingoxides of nitrogen. Such catalyst materials may include, for example,aluminum, platinum, rhodium, barium, cerium, and/or alkali metals,alkaline-earth metals, rare-earth metals, or combinations thereof. Thecatalyst materials may be situated within the NOx trap 35 so as tomaximize the surface area available for NOx absorption, and the catalystmaterials may be located on a substrate of the NOx trap 35. Substrateconfigurations may include, for example, a honeycomb, mesh, or any otherconfiguration known in the art. The NOx trap 35 may be capable ofstoring NOx over a wide range of exhaust temperatures and may beconfigured to store NOx at relatively low exhaust temperatures, such as,for example, below 200 degrees Celsius. Such exhaust temperatures mayoccur during power source start-up or in low-load operating conditions.For example, it may be difficult for the SCR catalyst 19 to reduce orotherwise convert NOx at such low temperatures; thus, the NOx trap 35may be particularly helpful in meeting government NOx emissionsregulations at low temperatures. The NOx trap 35 may, however, store NOxmore effectively at elevated exhaust temperatures. For example, theability of the NOx trap 35 to adsorb NOx may be maximized when theexhaust gas temperatures between approximately 300 degrees Celsius andapproximately 400 degrees Celsius. Accordingly, in an exemplaryembodiment, the NOx trap 35 may be fluidly connected proximate an outlet43 of the power source 12 such that the exhaust gases entering the NOxtrap 35 may undergo relatively little convective cooling. It isunderstood that the outlet 43 may be an outlet of an exhaust manifold ofthe power source 12.

The energy extraction assembly 22 may be configured to extract energyfrom, and reduce the pressure of, the exhaust gases produced by thepower source 12. The energy extraction assembly 22 may be fluidlyconnected to the power source 12 by one or more flow lines 15 and mayreduce the pressure of the exhaust gases to any desired pressure. Theenergy extraction assembly 22 may include one or more turbines 14,diffusers, or other energy extraction devices known in the art. In anexemplary embodiment wherein the energy extraction assembly 22 includesmore than one turbine 14, the multiple turbines 14 may be disposed inparallel or in series relationship. It is also understood that in anembodiment of the present disclosure, the energy extraction assembly 22may alternatively be omitted. In such an embodiment, the power source 12may include, for example, a naturally aspirated engine. As will bedescribed in greater detail below, a component of the energy extractionassembly 22 may be configured in certain embodiments to drive acomponent of the compression assembly 32. It is understood that, in anexemplary embodiment, the energy extraction assembly 22 may include aheat exchanger and/or other components required to form and/orfacilitate, for example, a Rankine cycle or a Brayton cycle.

In an exemplary embodiment, the regeneration device 20 of the exhausttreatment system 10 may be fluidly connected to the energy extractionassembly 22 via flow line 15 and may be configured to increase thetemperature of an entire flow of exhaust produced by the power source 12to a desired temperature. The desired temperature may be, for example, aregeneration temperature of the filter 16. Accordingly, the regenerationdevice 20 may be configured to assist in actively regenerating thefilter 16. Alternatively, in another exemplary embodiment, theregeneration device 20 may be configured to increase the temperature ofonly a portion of the entire flow of exhaust produced by the powersource 12. The regeneration device 20 may include, for example, a fuelinjector and an ignitor (not shown), heat coils (not shown), and/orother heat sources known in the art. Such heat sources may be disposedwithin the regeneration device 20 and may be configured to assist inincreasing the temperature of the flow of exhaust through convection,combustion, and/or other methods.

As shown in FIG. 1, the filter 16 of the exhaust treatment system 10 maybe connected downstream of the regeneration device 20. The filter 16 mayhave a housing 25 including an inlet 23 and an outlet 31. In anexemplary embodiment, the regeneration device 20 may be disposed outsideof the housing 25 and may be fluidly connected to the inlet 23 of thehousing 25. In another exemplary embodiment, the regeneration device 20may be disposed within the housing 25 of the filter 16. The filter 16may be any type of filter known in the art capable of extracting matterfrom a flow of gas. In an embodiment of the present disclosure, thefilter 16 may be, for example, a particulate matter filter positioned toextract particulates from an exhaust flow of the power source 12. Thefilter 16 may include, for example, a ceramic substrate, a metallicmesh, foam, or any other porous material known in the art. Thesematerials may form, for example, a honeycomb structure within thehousing 25 of the filter 16 to facilitate the removal of particulates.As discussed above, the particulates may be, for example, solubleorganic fraction, hydrocarbons, and/or soot.

In an exemplary embodiment of the present disclosure, a portion of theexhaust produced by the combustion process may leak past piston sealrings within a crankcase 45 of the power source 12. This portion of theexhaust, often called “blow-by gases” or simply “blow-by,” may containone or more of the exhaust gas components discussed above. In addition,because the crankcase 45 is partially filled with lubricating oil beingagitated at high temperatures, the blow-by gases may also contain oildroplets and oil vapor. The blow-by gases may build up within thecrankcase 45 over time, thereby increasing the pressure within thecrankcase 45. In such an embodiment, a ventilation line 42 may befluidly connected to the crankcase 45 of the power source 12.

The ventilation line 42 may comprise piping, tubing, and/or otherexhaust flow carrying means known in the art and may be structurallysimilar to the flow lines 15 described above. The ventilation line 42may include, for example, a check valve 44 and/or any other valveassembly known in the art. The check valve 44 may be configured toassist in controllably regulating a flow of fluid through theventilation line 42. The ventilation line 42 may be configured to directthe blow-by gases from the crankcase 45 to a location upstream of thefilter 16, such as, for example, a port 46 of the flow line 15. Forexample, the ventilation line 42 may assist in directing the portion ofexhaust gas from the crankcase 45 to a port 46 disposed upstream of theregeneration device 20. By directing the blow-by gases upstream of thefilter 16 and/or the regeneration device 20, the contaminants containedin the blow-by gases may be substantially removed without contaminatingthe supercharger, turbocharger, or various power source components.

The oxidation catalyst 18 of the exhaust treatment system 10 may belocated between the regeneration device 20 and the filter 16, and maycontain catalyst materials useful in collecting, absorbing, adsorbing,and/or converting hydrocarbons, carbon monoxide, and/or oxides ofnitrogen contained in a flow. Such catalyst materials may include, forexample, aluminum, platinum, palladium, rhodium, barium, cerium, and/oralkali metals, alkaline-earth metals, rare-earth metals, or combinationsthereof. The catalyst materials may be situated within the oxidationcatalyst 18 so as to maximize the surface area available for thecollection and/or conversion of the flow components discussed above. Theoxidation catalyst 18 may include, for example, a ceramic substrate, ametallic mesh, foam, or any other porous material known in the art, andthe catalyst materials may be located on, for example, a substrate ofthe oxidation catalyst 18. The oxidation catalyst 18 may, for example,assist in oxidizing one or more components of the exhaust flow, such as,for example, particulate matter, hydrocarbons, and/or carbon monoxide.The oxidation catalyst 18 may also be configured to oxidize NO containedin the exhaust gas, thereby converting it to NO₂. Thus, the oxidationcatalyst 18 may assist in achieving a desired ratio of NO to NO₂upstream of the SCR catalyst 19. As mentioned above, this desired ratiomay be, for example, approximately one to one.

As illustrated in FIG. 2, in an additional exemplary embodiment of thepresent disclosure, a filter 36 of the exhaust treatment system 100 mayinclude catalyst materials useful in collecting, absorbing, adsorbing,and/or converting hydrocarbons, carbon monoxide, and/or oxides ofnitrogen contained in a flow. In such an embodiment, the oxidationcatalyst 18 (FIG. 1) may be omitted. The catalyst materials may include,for example, any of the catalyst materials discussed above with respectto the oxidation catalyst 18 (FIG. 1). The catalyst materials may besituated within the filter 36 so as to maximize the surface areaavailable for collection and/or conversion. For example, the catalystmaterials may be located on a substrate of the filter 36. The catalystmaterials may be added to the filter 36 by any conventional means, suchas, for example, coating or spraying, and the substrate of the filter 36may be partially or completely coated with the materials.

In the embodiment shown in FIG. 2, the catalyst materials disposed onthe substrate of the filter 36 may assist in passively regenerating thefilter 36 during power source operation. As the power source 12operates, particulates and other components of the power source exhaustmay be trapped by the filter substrate. The exhaust flow may reachtemperatures in excess of, for example, 300 degrees Celsius duringnormal operation of the power source 12 (i.e., without operating thepower source 12 in a manner so as to increase the temperature of theexhaust by, for example, wastegating or other conventional methods), andthe exhaust gas may increase the temperature of at least a portion ofthe filter substrate through convective heat transfer. At suchtemperatures, the components of the power source exhaust trapped by thesubstrate of the filter 36 may begin to react with the catalyst materiallocated on the substrate. In particular, the catalyst material maypassively regenerate a portion of the filter 36 by oxidizing particulatematter trapped by the filter substrate as well as carbon monoxide and/orhydrocarbons contained in the exhaust flow. Oxidation may occur at apassive regeneration temperature of the filter 36 in which the catalystmaterial is hot enough to react with the components of the exhaust flowwithout additional heat being provided by, for example, the regenerationdevice 20. Such passive regeneration temperatures may be below theactive regeneration temperature of the filter 36.

Although at least a portion of the particulate matter contained withinthe filter 36 may be oxidized and/or removed therefrom through passiveregeneration, it is understood that, as shown in FIG. 2, an exemplaryexhaust treatment system 100 of the present disclosure may, nonetheless,include a regeneration device 20. Utilizing a catalyzed filter 36 inconjunction with a regeneration device 20 may assist in increasing theinterval between active regenerations. Increasing this interval mayreduce the amount of, for example, fuel burned during operation of thepower source 12 and, thus, may reduce the cost of operating the machineto which the power source 12 is connected. An exhaust treatment system100 including both a catalyzed filter 36 and a regeneration device 20may also enable filter manufacturers to include less catalyst material(such as, for example, precious metals) in the filter 36, therebyreducing the cost of the filter 36 and the overall cost of the exhausttreatment system 100.

Referring again to FIG. 1, the SCR catalyst 19 of the exhaust treatmentsystem 10 may be any selective catalytic reduction catalyst known in theart and may be, for example, a urea-based or an ammonia-based catalyst.The SCR catalyst 19 may be, for example, a vanadium and titanium-type, aplatinum-type, or a zeolite-type SCR catalyst, and may include asubstrate containing one or more of these metals and configured toassist in reducing NOx. For example, the SCR catalyst 19 may be capableof maintaining the NOx emissions of the exhaust treatment system 10below approximately 0.2 grams/horsepower-hour, in compliance with futuregovernment regulations. The SCR catalyst 19 may have an optimum or peakNOx conversion rate when the ratio of NO to NO₂ entering the SCRcatalyst 19 is approximately one to one. The SCR catalyst 19 may be mosteffective at temperatures between approximately 200 degrees Celsius andapproximately 500 degrees Celsius. As used herein, the term “conversionrate” is defined as the rate at which NOx is catalytically converted toN₂ through a reduction reaction.

As mentioned above, the SCR catalyst 19 may be configured to reduce NOxin the presence of a reductant, such as, for example, urea or ammonia.Accordingly, the exhaust treatment system 10 may include an injector 37,a pump 39, a storage device 41, and/or any other components required todeliver reductant upstream of the SCR catalyst 19 and/or otherwisefacilitate NOx reduction. In an exemplary embodiment, the injector 37may be any type of fluid injector configured to deliver a flow ofaqueous reductant. The injector 37 may be configured to at leastpartially atomize the flow of reductant as it is delivered, therebyfacilitating mixing of the reductant with, for example, an exhaust flowof the power source 12. The pump 39 may be configured to draw reductantfrom the storage device 41 and pressurize the reductant upstream of theinjector 37. Although not shown in FIG. 1, it is understood that one ormore control valves maybe used in conjunction with the pump 39 to meterthe flow of reductant supplied to the injector 37. Moreover, the controlvalves, pump 39, and/or the injector 37 may be electrically connected toand controlled by a controller (not shown).

As shown in FIG. 1, the clean-up catalyst 33 may be fluidly connecteddownstream of the SCR catalyst 19. The clean-up catalyst 33 may beconfigured to capture, store, and/or convert unreacted reductants thatmay slip past the SCR catalyst 19. In addition, it is understood that insome operating conditions, a quantity of NOx carried by the exhaust flowmay not be converted to N₂ by the SCR catalyst 19. Such conditions mayinclude, for example, when the SCR catalyst 19 is below the optimum NOxconversion temperature range discussed above (between approximately 200degrees Celsius and approximately 500 degrees Celsius), when the ratioof NO to NO₂ is not approximately one to one, and when substantially allof the NOx conversion sites of the SCR catalyst substrate are occupied.In such conditions, the clean-up catalyst 33 may also assist in, forexample, collecting and/or storing NOx. In an exemplary embodiment, theclean-up catalyst 33 may be an NOx trap similar to the NOx trap 35discussed above.

The recirculation line 24 may be disposed between the filter 16 and theSCR catalyst 19, and may be configured to assist in directing a portionof the exhaust flow from the filter 16 to the inlet 21 of the powersource 12. As discussed above, the recirculation line 24 mayalternatively be fluidly connected between the oxidation catalyst 18 andthe filter 16, between the SCR catalyst 19 and the clean-up catalyst 33,or downstream of the clean-up catalyst 33. The recirculation line 24 maycomprise piping, tubing, and/or other exhaust flow carrying means knownin the art, and may be structurally similar to the flow lines 15described above. The portion of the exhaust flow directed to the powersource 12 by the recirculation line 24 may assist in reducing theconcentration of oxygen within, for example, one or more combustionchambers of the power source 12 and may assist in increasing thespecific heat of the air/fuel mixture therein, thereby lowering themaximum combustion temperature within the one or more combustionchambers. The lowered maximum combustion temperature and reduced oxygenconcentration may slow the chemical reaction of the combustion processand decrease the formation of NOx by the power source 12.

The flow cooler 26 may be fluidly connected to the filter 16 via therecirculation line 24 and may be configured to cool the portion of theexhaust flow passing through the recirculation line 24. The flow cooler26 may include a liquid-to-air heat exchanger, an air-to-air heatexchanger, or any other type of heat exchanger known in the art forcooling an exhaust flow. In an alternative exemplary embodiment of thepresent disclosure, the flow cooler 26 may be omitted.

The mixing valve 30 may be fluidly connected to the flow cooler 26 viathe recirculation line 24 and may be configured to assist in regulatingthe flow of exhaust through the recirculation line 24. It is understoodthat in an exemplary embodiment, a check valve (not shown) may befluidly connected upstream of the flow cooler 26 to further assist inregulating the flow of exhaust through the recirculation line 24. Themixing valve 30 may be a spool valve, a shutter valve, a butterflyvalve, a check valve, a diaphragm valve, a gate valve, a shuttle valve,a ball valve, a globe valve, or any other valve known in the art. Themixing valve 30 may be actuated manually, electrically, hydraulically,pneumatically, or in any other manner known in the art. The mixing valve30 may be in communication with the controller mentioned above (notshown) and may be selectively actuated in response to one or morepredetermined conditions.

The mixing valve 30 may also be fluidly connected to an ambient airintake 29 of the exhaust treatment system 10. Thus, the mixing valve 30may be configured to control the amount of exhaust flow entering a flowline 27 relative to the amount of ambient air flow entering the flowline 27. For example, as the amount of exhaust flow passing through themixing valve 30 is desirably increased, the amount of ambient air flowpassing through the mixing valve 30 may be proportionally decreased andvice versa.

As shown in FIG. 1, the flow sensor 28 may be fluidly connected to therecirculation line 24 downstream of the flow cooler 26. The flow sensor28 may be any type of mass air flow sensor, such as, for example, a hotwire anemometer or a venturi-type sensor. The flow sensor 28 may beconfigured to sense the amount of exhaust flow passing through therecirculation line 24. It is understood that the flow cooler 26 mayassist in reducing fluctuations in the temperature of the portion of theexhaust flow passing through the recirculation line 24. Reducingtemperature fluctuations may also assist in reducing fluctuations in thevolume occupied by a flow of exhaust gas since a high temperature massof gas occupies a greater volume than the same mass of gas at a lowtemperature. Thus, sensing the amount of exhaust flow through therecirculation line 24 at positions downstream of the flow cooler 26(i.e., at a relatively controlled temperature) may result in moreaccurate flow measurements than measurements taken upstream of the flowcooler 26. It is further understood that the flow sensor 28 may alsoinclude, for example, a thermocouple (not shown) or other deviceconfigured to sense the temperature of the exhaust flow.

The flow line 27 downstream of the mixing valve 30 may direct theambient air/exhaust flow mixture to the compression assembly 32. Thecompression assembly 32 may include a compressor 13 configured toincrease the pressure of a flow of gas to a desired pressure. Thecompressor 13 may include a fixed geometry type compressor, a variablegeometry type compressor, or any other type of compressor known in theart. In the exemplary embodiment shown in FIG. 1, the compressionassembly 32 may include more than one compressor 13, and the multiplecompressors 13 may be disposed in parallel or in series relationship. Acompressor 13 of the compression assembly 32 may be connected to aturbine 14 of the energy extraction assembly 22, and the turbine 14 maybe configured to drive the compressor 13. In particular, as hot exhaustgases exit the power source 12 and expand against the blades (not shown)of the turbine 14, components of the turbine 14 may rotate and drive theconnected compressor 13. Alternatively, in an embodiment in which theturbine 14 is omitted, the compressor 13 may be driven by, for example,the power source 12, or by any other drive known in the art. It is alsounderstood that in a nonpressurized air induction system, thecompression assembly 32 may be omitted.

The aftercooler 34 may be fluidly connected to the power source 12 viathe flow line 27 and may be configured to cool a flow of gas passingthrough the flow line 27. In an exemplary embodiment, this flow of gasmay be the ambient air/exhaust flow mixture discussed above. Theaftercooler 34 may include a liquid-to-air heat exchanger, an air-to-airheat exchanger, or any other type of flow cooler or heat exchanger knownin the art. In an exemplary embodiment of the present disclosure, theaftercooler 34 may be omitted if desired.

The exhaust treatment system 10 may further include a condensate drain38 fluidly connected to the aftercooler 34. The condensate drain 38 maybe configured to collect a fluid, such as, for example, water or othercondensate formed at the aftercooler 34. It is understood that suchfluids may consist of, for example, condensed water vapor contained inrecycled exhaust gas and/or ambient air. In such an exemplaryembodiment, the condensate drain 38 may include a removably attachablefluid tank (not shown) capable of safely storing the condensed fluid.The fluid tank may be configured to be removed, safely emptied, andreconnected to the condensate drain 38. In another exemplary embodiment,the condensate drain 38 may be configured to direct the condensed fluidto a fluid container (not shown) and/or other component or location onthe machine. Alternatively, the condensate drain 38 may be configured todirect the fluid to the atmosphere or to the surface by which themachine is supported.

As shown in FIGS. 1 and 2, the recirculation line 24 may form a lowpressure EGR loop in which a portion of the exhaust gas is extracteddownstream of the energy extraction assembly 22 and directed to theinlet 21. It is understood, however, that in an exemplary embodiment,the recirculation line 24 may form a high pressure EGR loop. In such anembodiment, the portion of the exhaust gas may be extracted upstream ofthe energy extraction assembly 22. For example, as shown in FIGS. 3 and4, in additional exemplary embodiments, the recirculation line 24 may beconnected downstream of the NOx trap 35 and upstream of the energyextraction assembly 22. FIG. 3 illustrates an exemplary embodimentincluding an oxidation catalyst separate from and upstream of a filter36, and FIG. 4 illustrates an exemplary embodiment in which a filter 36includes a catalyzed substrate and in which the oxidation catalyst 18 isomitted.

In the high pressure EGR loop embodiments of FIGS. 3 and 4, therecirculated exhaust gas may pass through the flow cooler 26 upstream ofthe flow sensor 28. The recirculated exhaust gas may then be combinedwith a compressed flow of ambient air at the mixing valve 30, and thecombined flow may be directed to the aftercooler 34. It is understoodthat, in the high pressure EGR loop embodiments of FIGS. 3 and 4, one ormore components of the exhaust treatment system 200, 300 may be omitted.In another exemplary embodiment of a high pressure EGR loop (not shown),the recirculation line 24 may be internal to the power source 12,thereby creating an internal EGR loop. In such an embodiment, at leastthe flow cooler 26 may be omitted. In still another high pressure EGRloop embodiment, the recirculation line 24 may be fluidly connecteddownstream of the power source 12 and upstream of the NOx trap 35.

INDUSTRIAL APPLICABILITY

The exhaust treatment systems 10, 100, 200, 300 of the presentdisclosure may be used with any combustion-type device, such as, forexample, an engine, a furnace, or any other device known in the art,where the reduction of NOx emissions, the reduction of particulatematter emissions, and/or the recirculation of treated exhaust into aninlet of the device is desired. The exhaust treatment systems 10, 100,200, 300 may be useful in reducing the amount of engine emissions (suchas, for example, NOx and particulate matter) discharged into theenvironment. The exhaust treatment systems 10, 100, 200, 300 may also becapable of purging the portions of the exhaust gas captured bycomponents of the system through a regeneration process.

The operation of the exhaust treatment systems 10, 100, 200, 300 willnow be explained in detail. Unless otherwise noted, the exhausttreatment system 10 of FIG. 1 will be referred to for the duration ofthe disclosure.

The power source 12 may combust a mixture of fuel, recirculated exhaustgas, and ambient air to produce mechanical work and an exhaust flow. Asdiscussed above, the exhaust flow includes a complex mixture of solid,liquid, and/or gaseous components. In general, the solid and liquidcomponents of the exhaust flow may consist of soot, soluble organicfraction, and unburned hydrocarbons. The soot produced during combustionmay include carbonaceous materials, and the soluble organic fraction mayinclude unburned hydrocarbons that are deposited on or otherwisechemically combined with the soot. The gaseous components of the exhaustflow may consist of, among other things, NOx and CO.

The exhaust flow may be directed, via flow line 15, from the powersource 12 through the NOx trap 35. The NOx trap 35 may store, absorb,adsorb, collect, and/or otherwise store NOx carried by the exhaust flow.The NOx trap 35 may be useful in removing NOx in, for example, low loador low temperature (start-up) operating conditions in which the SCRcatalyst 19 may be less effective in catalytically reducing NOx. Thereduced NOx exhaust may then be directed to the energy extractionassembly 22. The hot exhaust flow may expand on the blades of theturbines 14 of the energy extraction assembly 22, and this expansion mayreduce the pressure of the exhaust flow while assisting in rotating theturbine blades.

The reduced pressure exhaust flow may pass through the regenerationdevice 20 to the oxidation catalyst 18. The regeneration device 20 maybe deactivated during the normal operation of the power source 12. Asthe exhaust flow passes through the oxidation catalyst 18, the catalystmaterials contained therein may assist in oxidizing the particulatematter, hydrocarbons, and/or carbon monoxide carried by the flow. Thecatalyst materials may also assist in oxidizing gaseous NO contained inthe flow, thereby converting the NO to NO₂. The oxidation catalyst 18may be coated and/or otherwise configured to yield a treated flow ofexhaust having a desired ratio of NO to NO₂ to optimize the NOxconversion rate of the SCR catalyst 19. As discussed above, this desiredratio may be approximately one to one.

As the exhaust flow exits the oxidation catalyst 18 and passes throughthe filter 16, at least a portion of the particulate matter entrainedwith the exhaust flow may be captured by the substrate, mesh, and/orother structures within the filter 16. As discussed above with respectto FIG. 2, in an exemplary embodiment, the catalyst materials of theoxidation catalyst 18 may be disposed on the substrate of the filter 36and, in such an embodiment, the oxidation catalyst 18 may be omitted.Such a configuration may also allow for the passive regeneration of thefilter 36 during operation of the power source 12.

With continued reference to FIG. 1, a portion of the filtered exhaustflow may be extracted downstream of the filter 16 and the remainder ofthe filtered exhaust flow may be directed to the SCR catalyst 19.Disposing the filter 16 upstream of the SCR catalyst 19 minimizes theamount of, for example, particulate matter entering the SCR catalyst 19,thereby reducing the fouling thereof. The injector 37 may inject adesirable quantity of reductant into the exhaust flow upstream of theSCR catalyst 19, and the amount of reductant injected may depend on,among other things, the mass flow, temperature, and NOx concentration ofthe filtered flow. The injection amount may be calculated and otherwisecontrolled by the controller mentioned above (not shown). The injectedreductant may be substantially atomized and may mix substantiallyuniformly with the filtered flow upstream of the SCR catalyst 19.

The NOx carried by the filtered flow may be catalytically reduced by theSCR catalyst 19 in the presence of the injected reductant. Inparticular, the NOx molecules may be substantially entirely convertedto, for example, N₂, CO₂, H₂O, and O₂ by the SCR catalyst 19, and theSCR catalyst 19 may be configured to reduce the overall NOx emissions ofthe exhaust treatment system 10 to below 0.2 grams/horsepower-hour. TheSCR catalyst 19 reduces NOx most effectively at temperatures betweenapproximately 200 degrees Celsius and approximately 500 degrees Celsius,and the conversion rate of the SCR catalyst 19 will be maximized whenthe ratio of NO to NO₂ is approximately one to one.

The clean-up catalyst 33 downstream of the SCR catalyst 19 may removeany unreacted reductant from the flow exiting the SCR catalyst 19. Afterpassing through the clean-up catalyst 33, the treated exhaust flow mayexit the exhaust treatment system 10 through an exhaust system outlet17.

In the low pressure EGR loop embodiments of FIGS. 1 and 2, the extractedportion of the exhaust flow discussed above may enter the recirculationline 24 downstream of the energy extraction assembly 22 and may berecirculated back to the power source 12. Alternatively, with referenceto FIGS. 3 and 4, in the exemplary high pressure EGR loop embodimentsdisclosed herein, a portion of the exhaust flow may be extractedupstream of the energy extraction assembly 22. With reference to FIG. 1,the recirculated portion of the exhaust flow may pass through the flowcooler 26. The flow cooler 26 may reduce the temperature of the portionof the exhaust flow before the portion enters the flow line 27. Themixing valve 30 may be configured to regulate the ratio of recirculatedexhaust flow to ambient inlet air passing through flow line 27. Asdescribed above, the flow sensor 28 may assist in regulating this ratio.

The mixing valve 30 may permit the ambient air/exhaust flow mixture topass to the compression assembly 32 where the compressors 13 mayincrease the pressure of the flow, thereby increasing the temperature ofthe flow. The compressed flow may pass through the flow line 27 to theaftercooler 34, which may reduce the temperature of the flow before theflow enters the inlet 21 of the power source 12. As discussed above,recirculating a portion of the exhaust flow back to the power source 12assists in reducing the overall NOx produce thereby.

Over time, soot produced by the combustion process may collect in thefilter 16 and may begin to impair the ability of the filter 16 to storeparticulates. The flow sensor 28 and other sensors (not shown) senseparameters of the power source 12 and/or the exhaust treatment system10. Such parameters may include, for example, engine speed, enginetemperature, exhaust flow temperature, exhaust flow pressure, andparticulate matter content. The controller (not shown) may use theinformation sent from the sensors in conjunction with an algorithm orother preset criteria to determine whether the filter 16 has becomesaturated and is in need of regeneration. Once this saturation point hasbeen reached, the controller may send appropriate signals to componentsof the exhaust treatment system 10 to begin the regeneration process. Apreset algorithm stored in the controller may assist in thisdetermination and may use the sensed parameters as inputs.Alternatively, regeneration may commence according to a set schedulebased on fuel consumption, hours of operation, and/or other variables.

The signals sent by the controller may alter the position of the mixingvalve 30 to desirably alter the ratio of the ambient air/exhaust flowmixture. These signals may also activate the regeneration device 20.Upon activation, oxygen and a combustible substance, such as, forexample, fuel, may be directed to the regeneration device 20. Theregeneration device 20 may ignite the fuel and may increase thetemperature of the exhaust flow passing to the filter 16 to a desiredtemperature for regeneration. This temperature may be in excess of 700degrees Celsius (approximately 1,292 degrees Fahrenheit) in someapplications, depending on the type and size of the filter 16. At thesetemperatures, soot contained within the filter 16 may be burned away torestore the storage capabilities of the filter 16.

As discussed above, disposing the filter 36 upstream of the SCR catalyst19 may reduce or substantially eliminate fouling of the SCR catalyst 19caused by, for example, particulate matter carried by the exhaust flow.Minimizing SCR catalyst fouling may assist in maximizing the number ofavailable NOx conversion sites on the substrate of the SCR catalyst 19,thereby maximizing the ability of the SCR catalyst 19 to convert NOxcarried by the exhaust flow to, for example, N₂.

It is understood that systems employing an SCR catalyst for NOxconversion may provide for reduced NOx emissions to the environment. Forexample, as mentioned above, the SCR catalyst 19 may be capable ofmaintaining the NOx emissions of the exhaust treatment system 10described herein below approximately 0.2 grams/horsepower-hour, incompliance with future government regulations. Because the SCR catalyst19 is capable of obtaining such low levels of NOx emissions, reducingthe amount of NOx produced by the power source 12 by, for example,recirculating at least a portion of the exhaust gas, may no longer benecessary. Thus, due to the presence of the SCR catalyst 19, the EGRloop may instead be used to assist in improving, for example, the fueleconomy of the power source 12 and/or the exhaust treatment system 10,generally. In particular, a system combining an SCR catalyst with EGRmethods and components may enable the user to employ, for example, powersource control techniques to improve fuel economy. Such techniques mayinclude, for example, advancing fuel injection timing, modifying theactuation of combustion chamber intake valves, and/or altering fuel(rail) pressure.

In addition, recirculating a portion of the exhaust flow back to thepower source 12 may increase the amount of NO₂ produced by the powersource 12 during combustion. Such an increase may result in an exhaustflow having a higher ratio of NO₂ to NO at the outlet 43 of the powersource 12 than an exhaust flow produced by a power source of an exhausttreatment system not utilizing EGR. Obtaining this higher ratio of NO₂to NO through combustion may reduce the oxidation requirements of theoxidation catalyst 18 during operation. As a result, a smaller, lessexpensive oxidation catalyst 18 having less precious metals, may beused. The use of such an oxidation catalyst 18 may, thus, reduce theoverall cost of the exhaust treatment system 10 and may reduce theoverall footprint of the system 10 within, for example, a crowded enginecompartment of a machine to which the power source 12 is connected. Inaddition, obtaining this higher ratio of NO₂ to NO may be particularlyadvantageous at low temperatures (such as those occurring at start-up orduring low load conditions) where the ability of the oxidation catalyst18 to oxidize NO to NO₂ is diminished.

Other embodiments of the disclosed exhaust treatment system 10, 100,200, 300 will be apparent to those skilled in the art from considerationof the specification. For example, the system 10, 100, 200, 300 mayinclude additional filters, such as, for example, a sulfur trap,disposed upstream of the filter 16. The sulfur trap may be useful incapturing sulfur molecules carried by the exhaust flow. It is intendedthat the specification and examples be considered as exemplary only,with the true scope of the invention being indicated by the followingclaims.

1. An exhaust gas treatment system of an internal combustion engine,comprising: a selective catalytic reduction catalyst fluidly connectedto the internal combustion engine; an oxidation catalyst fluidlyconnected upstream of the selective catalytic reduction catalyst; aparticulate filter fluidly connected upstream of the selective catalyticreduction catalyst; and a recirculation line configured to direct aportion of an exhaust flow of the internal combustion engine toward aninlet of the engine.
 2. The system of claim 1, further including atleast one component configured to inject a flow of reductant upstream ofthe selective catalytic reduction catalyst.
 3. The system of claim 1,wherein the recirculation line is fluidly connected one of downstream ofthe oxidation catalyst, downstream of the particulate filter, ordownstream of the selective catalytic reduction catalyst.
 4. The systemof claim 1, wherein the recirculation line is fluidly connecteddownstream of an energy extraction assembly of the exhaust gas treatmentsystem.
 5. The system of claim 1, wherein the oxidation catalyst isdisposed on a substrate of the particulate filter.
 6. The system ofclaim 1, wherein the oxidation catalyst is configured to maintain adesired ratio of NO to NO₂ in an exhaust flow of the internal combustionengine.
 7. The system of claim 1, further including an NOx trap fluidlyconnected upstream of the oxidation catalyst.
 8. The system of claim 7,wherein the NOx trap is disposed between an outlet of the internalcombustion engine and an energy extraction assembly of the exhaust gastreatment system.
 9. The system of claim 1, further including a catalystfluidly connected downstream of the SCR catalyst.
 10. The system ofclaim 1, further including a ventilation line fluidly connected to acrankcase of the internal combustion engine.
 11. The system of claim 1,further including an energy extraction assembly configured to reduce thepressure of an exhaust flow of the internal combustion engine.
 12. Anexhaust gas treatment system of an internal combustion engine,comprising: a selective catalytic reduction catalyst fluidly connectedto the internal combustion engine; an oxidation catalyst fluidlyconnected upstream of the selective catalytic reduction catalyst; aparticulate filter fluidly connected upstream of the selective catalyticreduction catalyst; and a low pressure exhaust gas recirculation loop.13. The system of claim 12, wherein a component of the low pressureexhaust gas recirculation loop is fluidly connected one of downstream ofthe oxidation catalyst, downstream of the particulate filter, ordownstream of the selective catalytic reduction catalyst, and thecomponent is configured to direct a portion of an exhaust flow of theinternal combustion engine toward an inlet of the internal combustionengine.
 14. The system of claim 12, wherein the oxidation catalyst isdisposed on a substrate of the particulate filter.
 15. The system ofclaim 12, wherein the oxidation catalyst is configured to maintain adesired ratio of NO to NO₂ in an exhaust flow of the internal combustionengine.
 16. The system of claim 12, further including an NOx trapfluidly connected upstream of the oxidation catalyst.
 17. The system ofclaim 12, further including a catalyst fluidly connected downstream ofthe selective catalytic reduction catalyst.
 18. A method of an exhaustflow of an internal combustion engine, comprising: filtering the exhaustflow with a particulate filter; oxidizing the exhaust flow with anoxidation catalyst; catalytically reducing NOx contained in the filteredoxidized flow with a selective catalytic reduction catalyst; anddirecting a portion of the exhaust flow to an inlet of the internalcombustion engine.
 19. The method of claim 18, further includingcollecting NOx contained within the exhaust flow with an NOx trapfluidly connected upstream of the selective catalytic reductioncatalyst.
 20. The method of claim 18, further including removingreductant from the exhaust flow with a catalyst fluidly connecteddownstream of the selective catalytic reduction catalyst.